Mobile horizontal directional drilling (“HDD”) rigs conventionally include a horizontal directional drilling machine pivotally mounted on a tracked vehicle or tractor. Such mobile rigs generally provide a directional drill bit which is “steerable”, and which is mounted on the end of a flexible drill stem. Such a drill is often used for drilling holes, for instance, for installing flexible fiber-optic cable underground, for laying electric cable underground, or similar applications. The fact that the drill is steerable permits a user of the drill to drill under roadways, driveways, sidewalks, and similar, without disrupting the surface. With the conventional drilling machine described above, drilling operations usually are initiated at an angle of approximately 15 degrees to the horizontal. Once the drill bit is underground, it can be steered to drill a passageway of desired azimuth and then withdrawn when the work is completed.
It is necessary to anchor the rig prior to drilling. In addition to drilling torque forces, the drilling operations place push and pull back forces on the rig. These normal drilling forces cause reactionary forces on the rig that urge the rig to uproot or slide along the ground surface, for example. In conventional deployments, an anchor bar extends outwardly from the frame of the tractor and supports anchoring stakes. The anchoring stakes are driven into the support surface in an attempt to stabilize the drilling machine in place during drilling operations.
Larger mobile HDD rigs can deliver over 100,000 pounds of pull back force. Conventional anchoring systems for such larger rigs often further include anchoring piles driven into the ground. The piles may also be cemented. Smaller rigs may be anchored with rotary auger-like stakes driven into the ground with, for example, a hydraulic motor.
A typical anchoring setup has a main body portion which includes a stake-down plate. The stake-down plate is a rectangular metal plate, in which the front and rear long edges of the plate have been bent upwardly to make the stake-down plate have an elongated U-shape in cross-section from front to rear. The stake-down plate has top and bottom smooth surfaces, wherein metal stabilizers are welded to the top surface of the stake-down plate to give it rigidity.
The anchoring assembly also includes stakes which, as noted, can be screwed in or hydraulically driven into the ground or other support surface on which the anchoring assembly is positioned. The stakes may be screwed-in or driven into the support surface so as to be vertical or at an angle to horizontal. The stakes help anchor the anchoring assembly to the support surface in order to resist sliding of the drilling machine during drilling operations.
However, even with the stakes of the stake-down system of the anchoring assembly securely in place in the ground or other support surface, the advancing of the drill bit tends to create a force applied to the drill stem which urges movement of the tracked vehicle drilling machine with respect to the anchoring assembly. Furthermore, when withdrawing the drill bit, there is also a tendency to urge movement of the tracked vehicle drilling machine with respect to the anchoring assembly.
In some drilling applications, it is not possible or desirable to drive the stakes into the ground. The earth may be frozen or there may be electrical cable or similar directly beneath the intended staking location. In these types of situations, the tendency of the drilling machine to slide is particularly troublesome.
The prior art discloses various types of anchoring. U.S. Pat. No. 6,257,350 discloses a multiple-position stake-down assembly positioned beneath the HDD drive head. An anchoring regime is selectable at the stake-down assembly. U.S. Pat. No. 6,131,674 discloses a stake-down assembly positioned beneath the drive head, with additional gripping mechanisms deployed to oppose sliding forces on the stake-down assembly when the HDD rig exerts push and pull back forces. U.S. Pat. No. 5,709,276 discloses a rig anchoring system attached to the front of the rig itself. U.S. Pat. Nos. 5,253,721, 5,231,899 and 4,953,658 disclose conventional stake anchoring systems for smaller rigs. U.S. Pat. No. 4,023,828 discloses a cleat pad for the underneath of outriggers on earthmoving equipment.
All of the foregoing examples of the prior art overlook using the dead weight of the HDD rig itself to hold an anchoring system in the ground. For example, a mobile (track-driven) HDD rig capable of delivering over 100,000 pounds of pull back force may typically have a dead weight of 100,000 pounds itself. It would be advantageous to utilize that dead weight as much as possible to counteract reactionary forces to torque and push/pull back forces encountered during HDD operations. Therefore, there exists a need for an anchoring system that can harness that dead weight and use it to prevent the rig anchors from uprooting or sliding, for example, during push or pull back operations.